The effect of acidity on the catalytic action of PdCu zeolites in the oxidation of ethylene to acetaldehyde
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The acidity determines the activity of PdCu ion-exchange catalyst based on type A, X, and Y zeolites and mordenite in the oxidation of ethylene to acetaldehyde. Increasing the concentration of acidic OH groups in the PdCuNaY catalyst through decationization reduces the activity, selectivity, and stability of the catalyst.
IR studies have shown that NH3, introduced into the PdCu zeolite either through adsorption or as part of Pd(NH3) 4 2+ complexes, can interact with either the acidic H+ centers of the aluminosilicate crystals or with the transition-metal cations. There is the possibility of a redistribution of NH3 between the NH 4 + ions and the M(NH3) X 2+ faujasite complexes.
The reversible poisoning of PdCu zeolites by ammonia is due, in the first instance, to the formation of ammoniacal complexes with the palladium cations. Increasing the acidity of the PdCu zeolite reduces the deactivating action of ammonia.
KeywordsOxidation Acetaldehyde Ammonia Zeolite Acidity
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